high Idle problem again please help...

[ertech]

Hi
my car is a 89 930 USA .In the past I had a high idle after engine was hot and comming to a stop . I double checked all I think , pinched the aar and no difference . went to a Porsche specialist and he saw my 02 was unplugged and plugged it back and the problem went away .till now 3 weeks later . same problem . when i disconnect the 02 the idle goes even higher???from the board everyone says we can unplug the 02 with no effect why is this different on my car?
Thanks